In patent document 1, coils are formed by performing edgewise bending as shown in FIG. 3 of patent document 1. Further, as shown in FIGS. 2, 6, and 8 of patent document 1, the coil ends include peak portions formed to be crank-shaped. As a result, in a state in which the coil ends are overlapped in the axial direction of a stator, interference is avoided in the axial direction.
In patent document 2, coils are formed by performing flatwise bending as shown in FIG. 14 of patent document 2. Further, as shown in FIG. 16 of patent document 2, in a coil, a portion that joins a slot insertion portion and a connection portion of a coil end includes two twisted sections. Further, as shown in FIG. 2 of the patent document 2, coil end portions are overlapped with one another in the radial direction of a stator (that is, shaped so as not to interfere in the radial direction of the stator).
As shown in FIG. 32, a stator core 71 in patent document 3 includes a plurality of slots 71a, which are formed at predetermined intervals, and a plurality of coils 72, each coupled to two of the slots 71a. Each slot 71a includes an opening directed inward in the radial direction. The opening has a smaller width than a portion of the slot 71a located inward from the opening. Each coil 72 includes a first side 72a and second side 72b, each having a first end and a second end, a third side 72c, which is continuous with the first ends of the first and second sides 72a and 72b, and a fourth end 72d, which is continuous with the second ends of the first and second sides 72a and 72b. The first and second sides 72a and 72b are stacked to form an aligned winding to have a thickness allowing for insertion into two slots 71a. The third side 72c, which is located at a position shifted from the first and second sides 72a and 72b in the extending direction of the first and second sides 72a and 72b, is stacked to have a width that is smaller than the width of the opening of the slot 71a in a direction perpendicular to the stacking direction. The third side 72c passes by the opening of the slot 71a to arrange the first and second sides 72a and 72b in the two slots and couple the first and second sides 72a and 72b to the stator core 71.
Further, patent document 4 discloses a method for manufacturing a stator that prepares a plurality of coils in advance, inserts a first side of each coil into one of a plurality of slots in a stator core, and then inserts a second side of each coil into another one of the slots so that the coils are spirally overlapped as viewed from an end surface of the stator core. In the method of patent document 4, a holding jig, which has an outer circumference including a plurality of slit-shaped holding grooves of an integral multiple of the slot pitch of the stator core, is used to attach a plurality of coils, which are formed in advance, to the stator core. In a state in which a first side of each coil is arranged at an outer side of the holding jig and a second side is arranged in the holding groove, each coil is arranged along the circumference of the holding jig. Further, an auxiliary jig, which includes a plurality of blades corresponding to inner teeth of the stator core, is arranged on the end surface of the holding jig, and the first side of each coil is held in a gap of the corresponding first blade. The combination of the holding jig and the auxiliary jig is inserted into the stator core from the auxiliary jig, and the first side of each coil is guided by the auxiliary jig and inserted into the corresponding slot of the stator core by an edge of the holding jig. The holding jig arranged inside the stator core in this manner is pivoted by a predetermined angle to position the holding grooves in alignment with the corresponding slots. Then, the second side of each coil is pushed outward in the radial direction by a pushing portion and inserted into the corresponding slot of the stator core.